The present invention relates to tool holders in which coolant fluid is transmitted through the holder to a tool. Such tool holders provide a transmission of driving force (rotation) from a machine tool spindle as well as holding on retention of the tool. The present invention is more particularly related to a tap driving apparatus having a coolant fluid delivery system to a tap (or tapping tool) which is used to cut threads in holes in a work piece.
In such systems, a tap driving apparatus typically includes a floating mounting or holder in which springs mount the tap to the apparatus to allow the tap to follow the tap lead into the workpiece. A light spring provides a mounting in a tension direction on the tap, and a spindle is fed (advanced) at a rate of approximately 90 percent of the tap lead, so that the tap can pull ahead of the spindle feed and follow its lead, independent of the spindle feed. In such cases, it is not desirable to put a high axial force or a thrust on the tool (as could be applied by pressurized coolant), because such an axial force would defeat the floating mounting concept by forcing the tool into its forward stop where there is no float.
Examples of tool holders including a floating mounting are shown in U.S. Pat. Nos. 2,981,544 and 2,533,758, but these tool holders lack a through coolant fluid delivery system, and there has been no simple but effective way to add such a system to tap driving tool holders without destroying the floating feature.
Coolant fluid, supplied to the cutting tool through an internal passage in the cutting tool from a rear shank to a forward cutting portion, allows cooling of the cutting edges and a flushing out of chips created during cutting. Cooling and cleaning accomplished by the coolant fluid extends the life of the tool and allows driving the tool at a higher rotational speed.
In some tool holders, coolant fluid is "side-fed" into a reservoir extending around the tool shank at its rear end. This type of tool cooling system is shown generally in U.S. Pat. Nos. 3,024,030 and 3,791,660. In many applications such a delivery system is acceptable and presents few problems. It does require seals to isolate the fluid. However, in a tap driving apparatus, the tension part of the tension-and-compression "float" arrangement may be defeated by the pressurized coolant, which typically is delivered in the 500 to 1,000 psi range. Pressure, which is necessary to move the coolant forward to the cutting tip, tends to move the tool to its forward limit also, defeating the float. Such operation of pressurized coolant delivery system is undesirable in such applications.
Some prior art systems couple the coolant fluid to the tool through "O" rings (or other sealing type components) located at the tool/tool holder interface. These "O" rings engaging the tool are undesirable in some applications as they create parts to fail and wear out, requiring periodic replacement. Failure of the "O" rings can lead to tool holder failure through coolant leakage. It is important that coolant fluid be isolated from the tap drive mechanism, particularly the tension-and-compression float.
Some of the prior art systems additionally do not have an effective method for compensating for wear of the components and thus require a periodic adjustment and/or reconstruction to avoid fluid leakage and other undesirable effects.
In some other instances of coolant tools, it is necessary to use a collet to hold a tool within the tool holder and to fill collet slots with a rubber or other sealing compound to seal coolant fluid reservoir within the collet from leaking. This filling of collet slots is time consuming, adds expense, and is undesirable in that it restricts the ability to freely change tools and requires frequent resealing.
Other limitations and disadvantages of the prior art tool holders and coolant fluid delivery systems will be apparant to one skilled in the art in view of the following detailed description of the present invention and the accompanying drawings.